Interest in the development of new polyaromatic ethers, thioetbers, and amines, and routes for the synthesis of such compounds is increasing because of the useful chemical and physical properties they possess.
Polyaromatic ethers, thioethers and amines belong to a class of materials known as engineering thermoplastics, which are known to have desirable characteristics such as thermooxidative and dimensional stability, good mechanical properties, and resistance to high energy radiation. These materials are also known to be tough, creep resistant, and to exhibit good flexural, and tensile properties. Aromatic polymers find application in mouldings, coatings, adhesives, membranes and composite matrices.
Conventional cyclic polyethers are important synthetic targets owing to their ability to selectively complex ions. Interest in these materials originates from the size and nature of their cavity, which dictates whether or not such materials are capable of binding to compounds. Although a great deal of attention has been directed toward the encapsulation abilities of conventional cyclic polyethers, there is a growing interest in the synthesis of cyclic aryl ethers (see, for example An et al., J. Org. Chem, 1993:58:7694; Inoue et al., J. Org. Chem., 1993, 58:5411; Janetka et at. J. Am. Chem. Soc. 1995:117:1058-10586). Cyclic aryl ethers are appealing since the rigidity and stability of their structures greatly reduces the compound's conformational freedom which may allow for chiral recognition or catalysis at high temperature or in hostile environments (Mullins et al., CHEMTECH August 1991:25). Mullins et at. (Polym. Preprints: Am. Chem. Soc. Div. Polym. Chem. 1991;32:174) reported that cyclic aryl ethers may be subjected to ring-opening polymerization to produce linear polyethers without the release of side-products.
Conventional cyclic polyether, thioether, and amine syntheses for the formation of macrocyclic compounds require the implementation of harsh reaction conditions in order to obtain the desired products in low yields. For nucleophilic aromatic substitution reactions, the presence of a strong electron-withdrawing group attached to a haloarene disadvantageously requires subsequent harsh chemical reactions to remove the electron-withdrawing group once the reaction is complete, which may lead to destruction of the product formed.
Known methods for preparation of aromatic polyethers include the Ullmann ether synthesis, the Scholl reaction, nickel-catalysed homocoupling, conventional nucleophilic aromatic substitution, and polycondensation (for example, Cozan et al., J. Macromol. Sci. Pure Appl. Chem., 1993, 30:899). These methods may employ elevated temperatures, copper salts or oxides as catalysts, and in some cases, electron-withdrawing groups are bound to a reactant as required to force the reaction. These factors, along with the low reaction yield in some of these methods have resulted in a demand for a more efficient synthetic strategy.
The complexation of chloroarene to a metallic moiety in the activation of the aromatic ring toward nucleophilic aromatic substitution is known (see Pearson et al., J. Org. Chem. 1995; 60:281-284). This methodology enables preparation of a number of oligomeric ethers, thioethers and amines under mild reaction conditions. Abd-El-Aziz et al. (Organometallics 1994;13:374 and J. Chem Soc. Dalton Trans 1995:3375) provide reports of synthetic strategies for preparing linear aryl ethers using dichlorobenzene cyclopentadienyl iron complexes. A chain having up to 35 pendent cyclopentadienyl iron moieties has been reported. However, these synthetic routes are not capable of easily forming cyclic aryl ethers, thioethers or amines.
Crown ethers are an example of known cyclic aryl ethers. The preparation of dibenzo crown compounds is achieved via the nucleophilic aromatic substitution reactions of (o-dichlorobenzene)-Cr(CO).sub.3 with diethylene glycol and bis(2-mercaptoethyl) ether (Baldoli et al; J. Chem. Soc. Chem Common. 1985:1181). Disadvantages of this particular synthetic method are the implementation of harsh reaction conditions and the need for a phase-transfer catalyst in order to obtain the desired products in rather modest yields.